This open-source application maps the information that your iPhone is recording about your movements. It doesn't record anything itself, it only displays files that are already hidden on your computer. If you run it on an OS X machine that you've been syncing with an iPhone or an iPad with cellular plan, it will scan through the backup files that are automatically made, looking for the hidden file containing your location. If it finds this file, it will then display the location history on the map.